Embodiments of this invention relate to high strength flooring compositions. Some embodiments relate to a flooring composition made using gypsum and one or more water reducing agents.
Both gypsum and cement are well known as construction materials. Gypsum is the principal component of the familiar wallboard, where is it faced with paper to provide strength and a smooth surface. Cement is used in various applications where its water resistance and hardness are important, such as in concrete structures. Cement is also used in building panels where its hardness and water resistance are important.
Gypsum is also known as calcium sulfate dihydrate, terra alba or landplaster. Plaster of Paris is also known as calcined gypsum, stucco, calcium sulfate semihydrate, calcium sulfate half-hydrate or calcium sulfate hemihydrate. Synthetic gypsum, which is a byproduct of flue gas desulfurization processes from power plants, may also be used. When it is mined, raw gypsum is found in the dihydrate form. In this form, there are approximately two water molecules of water associated with each molecule of calcium sulfate. In order to produce the hemihydrate form, the gypsum can be calcined to drive off some of the water of hydration by the following equation:CaSO4.2H2O→CaSO4.½H2O+3/2H2O
When mixed with water, the hemihydrate rehydrates to form an interlocking matrix of interlocking dihydrate crystals. Gypsum hydration occurs in a matter of minutes or hours compared to several days for cement. This makes gypsum an attractive alternative for cement for flooring applications if sufficient hardness and strength can be achieved in the gypsum.
Gypsum flooring compositions typically include a sand additive. The amount of sand added to a composition depends on a variety of factors. Generally, higher levels of sand are desirable for economic reasons since greater sand addition leads to increased slurry coverage per unit mass of gypsum. Higher sand compositions, however, also generally lead to lower final product strength.
So called “water reducing agents” are slurry additives useful to reduce the amount of water required per unit mass of gypsum and other materials. Examples of water reducing agents include plasticizers, dispersants, and viscosity modifiers. These agents can improve the fluidity and other properties of a gypsum slurry. Among other functions, they can disperse the molecules in solution so that they move more easily relative to each other and thereby improve the flowability of the entire slurry. So-called superplasticizers generally include sulfonated naphthalene formaldehyde or sulfonated melamine formaldehyde as well as new generation polycarboxylic ethers (PCE). Plasticizers generally function to prevent agglomeration through electrostatic repulsion. New technology PCE's, on the other hand, function to increase flow through steric stabilization.